Mobile communication systems have developed through first-generation analog AMPS (Advanced Mobile Phone Systems) and second-generation cellular/PCS (Personal Communication Service) scheme. Recently, third-generation IMT-2000 (International Mobile Telecommunication-2000) scheme which features a high-speed data transfer has been developed and commercialized.
The IMT-2000 scheme is divided into synchronous and asynchronous scheme. The synchronous IMT-2000 scheme is divided again into CDMA (Code Division Multiple Access) 2000 1x scheme and CDMA 2000 1xEV-DO scheme.
The CDMA 2000 1x scheme provides a data transmission service at a peak data rate of 144 kbps, which is much faster than 14.4 kbps or 57.6 kbps supported by existing IS-95A/B network, by using an IS-95C network that has been evolved from the IS-95A/B network. Furthermore, unlike the conventional IS-95A/B network for an exclusive use of a circuit network, the CDMA 2000 1x scheme employs a combination of a circuit network and a packet network. Accordingly, by using the CDMA 2000 1x scheme, the quality of existing voice services and WAP (Wireless Application Protocol) services can be improved and various multimedia services (AOD, VOD, etc.) can be offered.
The CDMA 2000 1xEV-DO scheme is further evolved from the CDMA 2000 1x scheme and is based on a HDR (High Data Rate) concept of Qualcomm Inc., to realize a high-speed packet transmission. The CDMA 2000 1xEV-DO scheme offers an exclusive use of a packet network and a high-speed data service supporting peak data rates of up to 2.4 Mbps on the forward link and up to 153.6 kbps on the reverse link.
However, due to the limit of available bandwidth, all active terminals in a cell cannot receive the data service of 153.6 kbps on the reverse link at the same time. Accordingly, the reverse link resource is managed by allocating a low-speed reverse link extra channel having a data transfer rate lower than 153.6 kbps to the active terminals that are currently communicating or by allocating a high-speed reverse link extra channel of 153.6 kbps to the active terminals by time division.
Recently, there has been proposed various methods to efficiently manage the reverse link resource. Widely employed in the CDMA 2000 1xEV-DO scheme is a method for using the amount of load that is generated by packets normally received from terminals or a method for using a measured rise-over-thermal (ROT) value.
The method for using the load amount involves the steps of measuring the amount of load generated by radio packets normally transmitted from terminals; and, if the load amount is small, increasing a reverse link and, if otherwise, lowering the reverse link rate. The measurement of the load amount is accomplished by using a RRI (reverse rate indicator) transmitted from each terminal in its own cell. Therefore, although a cell self-interference rate is sufficiently reflected, interference rates with other cells are not reflected. Thus, despite the advantage that the amount of load generated by active users who are carrying out communication and the resultant cell self-interference are exactly measured and sufficiently reflected, the method using the load amount cannot perform an accurate control of reverse link rate because it does not reflect the cell interferences with other cells.
Meanwhile, the method using a ROT value involves the steps of measuring a ROT value at each antenna end of a wireless base station and controlling a reverse link rate such that it is increased when the ROT value is small while it is lowered when the ROT value is great. Specifically, the ROT value is obtained by measuring an input signal power of demodulation end at each antenna end of the wireless base station and subtracting a thermal noise power of the mobile communication system from the measured demodulation end input signal power on a decibel (dB) scale. The ROT value is an important value in which a total quantity of received signal power within a radio bandwidth may be reflected. The method using the ROT value is advantageous in that the reverse link rate of terminals can be appropriately controlled because this method reflects cell interference with other cells as well as cell self-interference to thereby measure an overall received load.
Since, however, the cell self-interference or the interference with other cells may include interference components that have substantially no influence on actual call processing of a receiving end, the method using the ROT value have a problem that those interference components are also reflected when the input signal power is measured. As a result, the ROT value tends to be larger than a desired level, so that the terminals are controlled to lower their reverse link rates regardless of the number of active users that are communicating or the amount of load generated by the active users. Such unnecessary control may result in a reduction of a data throughput when a high-speed data processing is required on the reverse link in case of using a visual telephone or a CDMA 2000 1xEV-DO network. Moreover, since the reverse link rates are greatly reduced more than necessary in the environment where instantaneous surge interference components occur, a call drop may be resulted.
Therefore, there is an increasing demand for an inventive method capable of controlling a reverse link rate by way of reflecting only the interference components relevant to the actual call processing, to thereby further improve the quality of data transmission on the reverse link.